Question about Samyang 16mm f2 lens on crop sensor camera
I'm going to Yosemite in the summer and would like to do some astrophotography there, but am finding it difficult to choose a lens. I have a Canon EOS 60D and 700D and have am currently thinking the Samyang 16mm f2 because of its wide angle and wide aperture. I initially decided on the Samyang 14mm f2.8 but changed to the 16mm because it was specifically designed for APS-C sensors and the 14mm is not and would give a smaller field of view.
However, the product page on the Samyang website says that it has an equivalent focal length of 24mm on APS-C sensors. How can it not be 16mm on APS-C if it's a 16mm lens designed for APS-C sensors? Will it actually be 16mm when used on my two APS-C cameras or will it be 24mm? If it is 24mm then which lens would you suggest, the 14mm or 16mm?
Additionally, if you would recommend a better (< £300) lens for astrophotography for APS-C cameras then please say.